The present invention relates to a device for loading a three-knife trimmer with brochures, periodicals or like bound book blocks.
A three-knife trimmer is used for trimming the three non-bound edges of a book block, periodical or brochure. These products are thereby given their final format. The three-knife trimmer operates by means of side and front knives which cut diagonally against cutting rails according to the knife-edge and anvil principle, the three-side trimming being carried out in a trimming station. For this purpose the book blocks are fixed under pressure to the trimming table by a pressing ram and the side and front trimming is performed by phase-offset knife movements. The products can be processed singly or in a stack having a maximum stack height of up to 80 mm.
The three-knife trimmer is frequently coupled in a conveyor line to an adhesive binding line or to a book production line. The products are fed automatically to and from the trimmer via conveyor belts. To compensate for the performance differences of the coupled machines, a pre-stacking device is arranged upstream of the three-knife trimmer. Known from EP 0 887 157 A2, for example, is a pre-stacking device for a three-knife trimmer which is equipped with a magazine having two magazine intermediate shelves divided into two parts and horizontally movable for opening and closing, the upper magazine intermediate shelf being provided to form a counted stack of book blocks and the lower magazine intermediate shelf for cyclically discharging the formed stack on to a feeder table.
Known pre-stacking devices can be operated both in magazine mode and in counted stack mode. In counted stack mode the book blocks reach the upper magazine section singly while being photo-electrically counted. On reaching the preselected number the stack is deposited by opening the upper intermediate magazine shelf on the lower shelf located below it and from there is dispensed in a precisely timed manner to the delivery table, to be ejected and fed to the intake device of the three-knife trimmer. The counted stack mode is especially suited to processing thin (2–5 mm thick) and fragile book blocks. By switching off the intermediate shelves the device is converted to magazine operation. In the magazine, book blocks (from approx. 5 mm thick) supplied thereto fall directly on to the delivery table arranged below the magazine. A height-adjustable stack slider determines the stack height and transports the stack of book blocks into the intake device of the three-knife trimmer. The magazine mode is also suited to book blocks of appropriate thickness which are fed in an imbricated flow.
The performance of the known pre-stacking devices is limited with regard to the processing of thin book blocks. Because of their low product height, these cannot be fed to the three-knife trimmer in magazine mode but only in counted stack mode, in the form of a stack comprising a precisely counted number of book blocks. However, the counted stack mode requires book blocks to be individually fed, and individual feeding on conveyor belts can reliably execute a feed rate of only up to approx. 10 000 book blocks/hour because of excessive conveying speeds on curves and at transfer points. The delivery of the individually-supplied book blocks to the upper magazine section also becomes increasingly critical at this feed rate because the book blocks are thrown against the side wall of the magazine at excessive velocity. In addition, the time between two book blocks supplied is no longer sufficient for opening and closing the upper magazine intermediate shelf to transfer the formed stack to the lower magazine section.